Process for the packaging of product under vacuum and vacuum-packaging machine

ABSTRACT

A vacuum-packing machine has a vacuum chamber (1), a stop valve (10) arranged between the vacuum chamber and a vacuum pump (13), a vacuum sensor (17) connected to the vacuum chamber and an indicator (22) for the negative pressure in the vacuum chamber. An electronic circuitry (21) is connected between the vacuum sensor (17) and the indicator (22) and is designed in such a way that the electric voltage supplied thereto by the vacuum sensor (17) is converted into a continuous series of rectangular pulses. Evacuation of the chamber (1) is stopped when a predetermined pulse frequency or a deviation from a linear course of an evacuation curve is detected. Closure of the package in a vacuum can be closely adapted to the product concerned.

The present invention relates to a process for the packaging of productunder a vacuum, in which the product, which is located in a still openwrapper, is introduced into the interior of a vacuum chamber, in whichthe chamber is then evacuated, and in which the evacuation is terminatedand the wrapper of the product is closed as soon as the desired negativepressure has been reached.

In known vacuum-packaging machines, the evacuation of the interior of avacuum-packaging chamber is terminated after a time span has elapsed.Thereafter, the pack containing the product to be packaged is closed,and the machine can then be opened and the sealed product extracted fromthe latter.

In the known packaging machines, the end of the evacuation of thepackaging chamber is brought about, for example, in that the packagingspace is evacuated during a specific previously determined and set timespan. The length of this time span is derived from the experience of theperson operating the machine. However, considerable problems can arisehere. One of these problems is related to the fact that the product tobe packaged contains moisture. At the same time, it can quite easilyhappen that different pieces of the same product to be packaged, forexample of meat, have different quantities of moisture. After most ofthe air has been sucked off from the packaging space, moisture beginsincreasingly to escape from the product to be packaged. This moisture islikewise sucked off from the vacuum chamber as vapor by means of thevacuum pump. Although the vacuum in the packaging space has alreadyreached the necessary value, because the vacuum pump still continues torun, moisture is still extracted from the product. The latter continuesto lose weight during the further running of the pump, and this isundesirable.

In the abovementioned known method of evacuation, there is virtually nopossibility of taking into account properties of that particular pieceof product to be packaged which is located in the machine.

The object of the present invention is to indicate a process, in whichthe end of the evacuation can be brought about in dependence on theproperties of the particular piece of product to be packaged which islocated in the machine.

In the process of the generic type mentioned in the preamble, thisobject is achieved, according to the invention, as defined in acharacterizing clause of claim 1.

A packaging machine for carrying out this process is defined in claim 7.

Embodiments of the present invention are explained in more detail belowby means of the accompanying drawing. This drawing showsdiagrammatically a machine for carrying out the present process.

The accompanying drawing shows diagrammatically one of the machines, bymeans of which the present process can be carried out. This machinecomprises a vacuum chamber 1 which has a bottom part 2 and a top part 3.The bottom part 2 is stationary and the top part 3 can be articulated onthe bottom part 2, for example in the manner of a lid. The bottom part 2and the top part 3 can be of approximately dish-shaped design. A gasket4 is located between the end edges of the side walls of the bottom part2 and of the top part 3, so that a vacuum can be built up in such achamber 1.

Connected to the interior of the vacuum chamber 1 are, at one end, aworking line 5 and a measuring line 6. Connected to the portion 11 ofthe working line 5 directly adjacent to the vacuum chamber 1 is theoutlet of a ventilating valve 7, the inlet 8 of which opens into thesurrounding atmosphere. A shut-off valve 10 is interposed in the workingline 5, specifically in such a way that one of the orifices of thisvalve 10 is connected to the first portion 11 of the working line 5. Theopposite orifice of the shut-off valve 10 is connected, via a secondportion 12 of the working line 5, to a vacuum pump 13. The latter can,for example, be a rotary-slide vacuum pump.

The machine comprises, furthermore, a three-way valve 15. The reversibleconnection 16 of this valve 15 is connected to a vacuum sensor 17. Oneof the connectable connections 18 of the directional valve 15 isconnected to the vacuum pump 13 via a line 19. The other end of themeasuring line 6 is connected to the second of the connectableconnections 20. For the description of the actual mode of operation ofthe present machine, it is assumed that the slide of the directionalvalve 15 is located in a position, in which the reversible connection 16of the valve 15 is flow-connected to the second connectable connection20 of the directional valve 15. This position of the slide of thedirectional valve 15 is shown in the accompanying drawing. The valveslide is located in its right-hand position. In this position of thevalve slide, the vacuum sensor 17 is connected to the measuring line 6and therefore also to the interior of the vacuum chamber 1.

The vacuum sensor 17 is a piezo-resistive cell which measures theabsolute pressure relative to the vacuum. At 0 bar, that is to say inthe case of an absolute vacuum, the measuring cell 17 supplies thevoltage of 0 mV. At ambient pressure, that is to say at approximately 1bar, the measuring cell 17 supplies a voltage of approximately 100 mV.This voltage is a direct voltage, the magnitude of which depends, asstated, on the magnitude of the measured negative pressure.

Connected to the electrical output of the vacuum sensor 17 is anelectronic circuit arrangement 21 which is indicated diagrammaticallymerely as a block in the accompanying drawing. Connected to themeasuring output of this circuit arrangement 21 is an indicator unit 22which indicates the magnitude of the vacuum in the form of numerals. Aline 23 serving for actuating the shut-off valve 10 is connected to oneof the working outputs of the circuit arrangement 21. A further line 24connected to a corresponding output of the circuit arrangement 21 servesfor actuating the ventilating valve 7. The directional valve 15 too canbe controlled by the circuit arrangement 21 via a line 25, this line 25being connected to a respective output of the circuit arrangement 21.

In order to close product to be packaged, the latter is wrapped in awrapper made of a material closable by welding, and this still open packis introduced into the interior of the vacuum chamber 1, in such a waythat the side tabs of the packaging material are located between weldingbars of the vacuum chamber 1. The vacuum chamber 1 is then closed andevacuated. After the vacuum has reached the desired value in the vacuumchamber 1, the welding appliance is activated and the pack is closed inthe vacuum chamber 1. Atmospheric pressure can thereafter be restored inthe vacuum chamber 1, so that the vacuum chamber 1 can be opened,emptied and loaded with new product to be packaged which is to beclosed.

In the circuit arrangement 21, inter alia electrical voltage emittedcontinuously by the vacuum sensor 17 is converted into a continuoustrain or series of rectangular pulses. This pulse train thus has aspecific frequency. The said conversion takes place in such a way thatthe frequency of the pulses is proportional to the magnitude of theoutput voltage of the vacuum sensor 17 and therefore also to theabsolute pressure. If the magnitude of the output voltage from thevacuum sensor 17 changes, then the frequency of the pulse train alsochanges correspondingly. Such pulse trains are transmitted to furtherportions of the circuit arrangement 21, where they are evaluated andwhere they can be used to control the mode of operation of the machine.

The memory of circuit arrangement 21 stores values which correspond tothe individual values of the negative pressure in the vacuum chamber 1.These values are stored as indications of frequencies which correspondto the individual values of the negative pressure.

The time windows Z or gate times are generated in the circuitarrangement 21. These constitute time segments, during which pulsetrains are transmitted in the circuit arrangement 21. The circuitarrangement 21 is also designed so that the length of these time windowsor gate times can be changed.

The time windows or gate times are generated at time intervals T.Furthermore, the circuit arrangement 21 is designed so that the timeinterval T between two successive time windows can be changed.

The number of pulses of the respective frequency which are transmittedduring the respective time window serves inter alia for indicating themagnitude of the negative pressure in the vacuum chamber 1.

The conversion of the output voltage of the vacuum sensor 17 into apulse train, the frequency of the respective pulse train being in aspecific relation to the magnitude of the vacuum in the chamber 1,allows at least two methods of evacuation of the chamber 1, in which thetermination of the evacuation allows closer reference to that particularpiece of product to be packaged which is located in the vacuumchamber 1. In the first method of evacuation, the chamber 1 is evacuateduntil a predetermined desired value of the negative pressure is achievedin the latter. In the second method of evacuation, the chamber 1 isevacuated until moisture or vapors begin to rise out of the product tobe packaged.

In the first method of evacuation, the vacuum value at which evacuationis to be terminated is selected as a comparative value or as acomparative frequency from the memory of the circuit arrangement 21 andis fixed. During the evacuation, the frequency of the pulse seriesobtained from the signal supplied by the vacuum sensor 17 is comparedwith the selected value for the comparative frequency in the circuitarrangement 21. As soon as the signal emitted by the vacuum sensor 17has a frequency which is equal to the comparative frequency, theevacuation is stopped.

Those circuits in the circuit arrangement 21 which perform the saidsignal conversion are followed by that circuit in which the time windowsZ are generated. In the present regard, the time interval T between twosuccessive time windows Z is of no particular importance. The timewindows Z are necessary, so that samples of the signal emitted by thevacuum sensor 17, which are to be tested, can be obtained. The testcircuit can contain, for example, counters. In these circuits, thefrequency of the signal sample transmitted during the time window Z iscompared with the comparative frequency. If the frequency of thetransmitted signal pattern is equal to the comparative frequency, thismeans that the preselected vacuum has been reached in the chamber 1, andthat the evacuation of the chamber 1 can be stopped via the line 23. Theshut-off valve 10 is closed, with the result that the chamber 1 isuncoupled from the vacuum pump 13. The ventilating valve 7 is openedautomatically by the circuit arrangement 21 via the line 24. The chamber1 is filled with air, it can be opened, and so on and so forth.

It was already known to couple the termination of the evacuation of thevacuum chamber to the reaching of a specific value of vacuum in thevacuum chamber. However, a relatively simple vacuum sensor having adirect effect on the remaining parts of the packaging machine was usedfor this purpose. In this previously known machine, the evaluation ofthe output signal of the vacuum sensor was relatively rough, andtherefore the moment when the evacuation was stopped was subject to abroad spread. In the conversion of the output voltage of the vacuumsensor 17 to a pulse train, as is the case in the present subject, thefrequency of this pulse train moreover still being in the kHz range, thevalue of the vacuum in the chamber 1 can be recorded relativelyaccurately. Furthermore, the said conversion allows a relatively simpleand reliable evaluation of this signal.

The second method of evacuation is based on the knowledge that thepressure in the vacuum chamber 1 first decreases virtually continuouslyduring the evacuation of the latter, when only air alone is sucked offfrom the vacuum chamber 1. When most of the air has been sucked off fromthe vacuum chamber 1 and therefore also from the still open pack, themoisture begins to escape from the material of the product to bepackaged or to evaporate on the surface of the product. It is known fromexperience that the quantity of vapor forming from the moisture isdifferent from the quantity of air hitherto sucked off from the vacuumchamber 1. The generation of vapor proceeds relatively quickly, so that,when vapor forms, the pressure in the chamber 1 decreases more slowlythan when air alone is being sucked off. Consequently, during the escapeof moisture from the product, the pressure in the chamber 1 no longerdecreases continuously and not as quickly as hitherto.

In the present case, at the start of the pumping operation, the pressurein the vacuum chamber 1 first decreases virtually linearlly, when onlyair is sucked off from the chamber 1. This segment of a pumping curve isvirtually linear, and it has a specific slope. After most of the air hasbeen sucked off from the chamber 1, vapour begins to escape from theproduct to be packaged, the result of this being that the slope of thepumping curve becomes smaller than before during this pumping phase.Such a trend of the pumping curve can be monitored by means ofelectronic circuits.

In the present case too, the samples of the signal emitted by the vacuumsensor 17 pass from the latter, during the time windows Z, to the testcircuits where the frequency of the signal sample is determined. Thesetest circuits are supplemented by circuits which can store the result ofthe test of a signal sample, until the test of the subsequent signalsample is concluded. The results of the test of these two signal samplesare then compared with one another, in order to determine the differencein frequency between these two signal samples. This difference indicatesthe slope of the respective segment of the pumping curve. As long as thesuccessive differences are equal to one another, the virtually linearsegment of the pumping curve is concerned, that is to say only air issucked off. As soon as the difference between two signal evaluations issmaller than the difference previously determined, the pumping curveflattens, and this means that now only vapour and moisture is extractedfrom the product. The evacuation can be stopped, this being carried outin the way already described above.

As already stated, the frequency of the pulses, which are generated inthe circuit arrangement 21 as a result of the voltage emitted by thevacuum sensor 17, depends on the magnitude of the negative pressure inthe vacuum chamber 1. The decrease of pressure in the vacuum chamber 1causes the frequency of the pulses to drop with decreasing pressure.This means that the number of pulses per unit time drops. This means,furthermore, that a decreasing number of pulses is transmitted duringthe time window of constant length when the pressure in the vacuumchamber 1 drops, that is to say the frequency of the pulse trainsdecreases.

The said deviations from the initially constant decrease of pressure inthe vacuum chamber 1 are very slight, and they can scarcely be indicatedby the vacuum sensor 17 in such a way that these deviations could beused directly in order to control the work of the machine. As stated,the frequency of the pulses which are generated as a result of theoutput voltage from the vacuum sensor 17 is relatively high. It is inthe kHz range. This means that a relatively large number of pulsescorresponds to a relatively small change of negative pressure in thevacuum chamber 1. This considerable number of pulses can be detectedrelatively easily by the said circuits and can be used to control themode of operation of the machine.

When the said deviation from the constant decrease of the pulsefrequency is detected in the circuit arrangement 21, this is interpretedas meaning that the vacuum chamber 1 is empty of air and that onlymoisture would still be extracted from the product if the vacuum pump 13were to be allowed to continue to run. The circuit arrangement 21 isdesigned so that, via its outputs, it causes the welding appliance toweld the product pack, so that it terminates the further evacuation ofthe vacuum chamber 1, and so that it initiates or even executes measureswhich allow the vacuum chamber 1 to be opened and emptied. For thispurpose, for example the shut-off valve 10 is reversed via the line 23,so that the vacuum chamber 1 is uncoupled from the vacuum pump 13.Thereafter, the ventilating valve 7 can be opened by the circuitarrangement 21, after which the vacuum cheer 1 can be opened andemptied.

After the vacuum chamber 1 has been filled with new product to bepackaged, it is closed again. The ventilating valve 7 too is closed,whilst the shut-off valve 10 is opened. The vacuum chamber 1 is therebyconnected to the vacuum pump 13 again, and once more a constant decreaseof pressure in the vacuum chamber 1 first takes place. A furtherpackaging cycle can be carried out in the way described above.

The mode of operation described can be incorporated in the circuitarrangement 21 in the form of individually specified work programs. Theoperator then need only select a specific program by entering thedesired mode of operation of the machine into the latter, for examplevia a keyboard. This mode of operation is then carried out automaticallyby the machine.

However, depending on the particular situation, it may be necessary forthe evacuation not to be stopped immediately after the occurrence of aflattening in the pumping or vacuum curve, but for it to continue to runfor a selectable time span. This is achieved in the simplest way bychanging the time interval T between two successive time windows Z. Theinstruction incorporated in the circuit arrangement can state, forexample, that the evacuation is to be terminated when the differencebetween two successively conducted tests of signal samples amounts totwo or fewer units. The difference is always greater than two units inthe region of the steep segment of the pumping curve. If the evacuationis to be stopped immediately after the occurrence of the flattening ofthe pumping curve, then the time span T is selected as short, forexample T=0.03 sec. If the evacuation is to run for a further time afterthe occurrence of the flattening, then the said time span T can even beset at 5 sec.

The pulses transmitted during the time window are converted, in thecircuit arrangement 21, into signals which cause a corresponding numberto be indicated in the indicator device 22. The numerals 0 or 000 in theindicator device 22 stand for atmospheric pressure in the vacuumchamber 1. The numeral 999 stands for vacuum in the vacuum chamber 1. Inthe event of an absolute vacuum, the frequency of the measuring pulsesamounts to approximately 13 kHz and, at ambient temperature, toapproximately 110 kHz. The respective numeral between 0 or 000 and 999thus corresponds to a specific number of measuring impulses which istransmitted during the time window. If 13 kHz is subtracted from 110 kHzand this result is divided by 999, then, for example, 97 kHz correspondsto a digit between 000 and 999.

Since the indication in the indicator device 22 is coupled to thefrequency of the pulse signal from the vacuum sensor 17, it is alsopossible to follow visually on the indicator device 22 how the magnitudeof the vacuum in the vacuum chamber 1 changes.

So that an outstanding quality of the packagings is guaranteed at everymoment, measures must be taken to acquire information on the state ofthe machine which could impair the quality of the packs. This purpose isserved by, inter alia, calibrations which are carried out on themachine. There are two types of calibrations which are to be carriedout, namely calibration in terms of the magnitude of the ambientpressure and calibration in terms of the maximum obtainable vacuum.

The first type of calibration, in which the magnitude of the ambientpressure is taken into account, takes place with the lid 3 of the vacuumchamber 1 opened. This calibration can be carried out after eachswitch-on of the machine or else also after each packaging cycle. Forthis, the vacuum sensor 17 is connected to the interior of the openedvacuum chamber 1 via the directional valve 15, the slide of which is inits right-hand position, and the measuring line 6. The shut-off valve 10is closed during this, or it is closed for this purpose.

The vacuum sensor 17 supplies an electrical voltage, the magnitude ofwhich is constant, because the pressure in the vacuum chamber 1 isuniform and is equal to the ambient pressure. As a result of the outputvoltage of the vacuum sensor 17, the circuit arrangement 21 generates aspecific number of pulses, this number of pulses being constant, becausethe pressure is constant. The circuit arrangement 21 automaticallyensures the relation between the number of pulses supplied by the vacuumsensor and the numerals 0 or 000 in the indicator device 22. Should theindicator device 22 indicate a different numeral from 000 at the startof this calibration, then the width of the time window T or themagnitude of the gate time is changed by the circuit arrangement 21itself within the scope of this calibration. If the numeral 000 cannotbe obtained in the indicator 22 during a specific time, then it is to beassumed that, for example, the vacuum sensor 17 or the circuitarrangement 21 is defective, and a fault alarm appears.

In the second type of calibration, the maximum obtainable vacuum isdetermined. This calibration is expediently carried out after eachpackaging cycle. In order to carry out this calibration, the slide ofthe directional valve 15 is adjusted in such a way that the reversibleorifice 16 of the valve 15 is flow-connected to the first connectableconnection 18 of the valve 15. In this case, the vacuum sensor 17 isconnected to the vacuum pump 13 via the auxiliary line 19. The shut-offvalve 10 is closed during this calibration, so that the vacuum pump 13is connected only to the vacuum sensor 17. After a few seconds, the line19 would have to be evacuated as far as the vacuum sensor 17, and afterthe expiry of this time span the measurement of the vacuum by the vacuumsensor 17 commences.

The maximum vacuum obtainable by a vacuum pump of the type mentionedhere can amount to 0.5 mb. The vacuum pump has a still acceptable rangeover which it is considered still to be good. The limit of thistolerance range can be around 3 to 5 bar. If the vacuum, which isgenerated during this calibration, does not reach these values, then afault alarm is emitted.

This calibration of the vacuum pump can be carried out because, asalready stated, the values or frequencies corresponding to theindividual steps of the vacuum are stored in the circuit arrangement 21.In this calibration, the circuit arrangement 21 compares the signalssupplied by the vacuum sensor 17 with the stored vacuum values in theway already described.

In this case too, the circuit arrangement 21 attempts automatically tomake the relation between the signals supplied by the vacuum sensor 17and the numeral 9 or 999 in the indicator device 22. If this is notpossible for a few seconds, then a fault alarm is emitted automatically.

The execution of this calibration, although it takes placeautomatically, takes a few seconds. If the person operating this machinehas in the meantime initiated the next packaging cycle, the machinestops the calibration operation automatically. Measured values obtainedduring the preceding calibration are used for the run of this packagingcycle.

The explanation of the present process made reference to avacuum-packaging machine for bags. The said bags can, for example, betubular bags. However, this process can, in practice, be employed in anytype of vacuum-packaging machine. In this regard, attention may bedrawn, for example, to foil vacuum-packaging machines.

I claim:
 1. Process for machine-packaging a product under vacuumcomprising the steps of:(a) introducing the product, in an open wrapper,into the interior of a vacuum chamber to which a vacuum sensor isconnected, (b) evacuating the vacuum chamber, during which the vacuumsensor continuously emits an output voltage, the magnitude of whichchanges in proportion to the negative pressure in the chamber, c)converting the output voltage into a continuous train of rectangularpulses having a pulse frequency proportional to the magnitude of theoutput voltage, thereby reflecting the magnitude of the vacuum in saidchamber, d) monitoring the pulse frequency and comparing it to a storedfrequency that corresponds to a desired negative pressure, e)terminating the evacuation when the pulse frequency equals the storedfrequency, and f) sealing the wrapper.
 2. Process according to claim 1,wherein time windows are generated during which the rectangular pulsesare transmitted for comparison with the stored frequency, in that thelength of said time windows is variable, and in that the intervalsbetween two successive time windows is variable.
 3. Process according toclaim 1 wherein the time during evacuation is divided into alternatingtime windows and intervals, and wherein the pulse frequency is comparedwith the stored frequency during said time windows.
 4. Process accordingto claim 1, wherein during evacuation pressure change in the vacuumchamber is monitored creating a vacuum curve, and wherein the evacuationis terminated when a deviation from a predetermined vacuum curve hasbeen detected.
 5. Process according to claim 1, wherein sealing thewrapper occurs in the vacuum chamber, which is, thereafter, opened andemptied.
 6. Process according to claim 1 as a recurring packaging cycle,further comprising first calibration step to determine the magnitude ofthe ambient pressure, wherein the first calibration is carried out onceat the start of a series of packaging cycles or after each packagingcycle.
 7. Process according to claim 1 as a receiving packaging cycle,further comprising a second calibration step during which a maximumvacuum in the chamber is determined, wherein the second calibration iscarried out before each packaging cycle.
 8. Process according to claim2, wherein the rectangular pulses transmitted during the time windowsare converted into signals, which visually show the process results. 9.Process according to claim 4, wherein the train of rectangular pulses istransmitted during time windows of adjustable length and the pulsefrequency compound with the stored frequency, and wherein timeintervals, which alternate with the time windows, are adjustable. 10.Process according to claim 4, wherein the chamber is evacuated when thevacuum curve is linear and has a first slope, wherein the evacuation isterminated when said vacuum curve lessens in slope, and wherein theslope of the vacuum curve is monitored by an electronic circuit. 11.Process according to claim 10, wherein pulse frequencies of therectangular pulses transmitted during successive time windows arecompared with one another to determine the difference therebetween,which indicates the slope of a respective segment of the vacuum curve,and wherein the evacuation is stopped after said slope of a respectivesegment smaller than a corresponding slope of the predetermined vacuumcurve is detected.
 12. Process according to claim 11, wherein theevacuation is adjusted to stop following a time span after the detectionof the smaller slope by changing the time interval between twosuccessive time windows.
 13. Vacuum-packaging machine for carrying outthe process according to claim 1, comprising (a) a vacuum chamber, (b) ashut-off valve between the vacuum chamber and a vacuum pump, (c) avacuum sensor connected to the vacuum chamber, and (d) an electroniccircuit, connected to one end of the vacuum sensor, that (i) convertsoutput voltage emitted by the vacuum sensor into a series of rectangularpulses, whereby the frequency of these pulses is in proportion to themagnitude of the output voltage, (ii) compares the pulse frequency witha stored frequency corresponding to the negative pressure in the vacuumchamber at which the evacuation is to be terminated, and (iii) effectstermination of the evacuation when the pulse frequency equals the storedfrequency.
 14. Vacuum-packaging machine according to claim 13, theelectronic circuit comprises a memory, which stores the train of pulsesas frequencies, each of which corresponds to individual values of thenegative pressure.
 15. Vacuum-packaging machine according to claim 13,wherein electronic circuit includes a test circuit comprising counters,which compare the pulse frequency with the stored frequency. 16.Vacuum-packaging machine according to claim 13, wherein the electroniccircuit effects measurement of the negative pressure during a timewindow, and wherein the number of pulses transmitted during said timewindow indicates the magnitude of negative pressure in the vacuumchamber.
 17. Vacuum-packaging machine according to claim 13, wherein theelectronic circuit detects whether the pulse frequency changesconstantly or not, and wherein the circuit signals the change of thepulse frequency and transmits it to receiving the parts of the machinewhen the pulse frequency does not change constantly. 18.Vacuum-packaging machine according to claim 13, wherein a working linehaving first and second ends and a measuring line having first andsecond ends are connected by their first ends to the vacuum chamberinterior, wherein the working line has a first portion and a secondportion, between which a shut-off valve is interposed, whereby saidfirst portion includes the first end connected to the vacuum chamber andthe vacuum pump is connected to the second portion of the working linecomprising the second end, wherein an outlet of a ventilating valve isconnected to the first portion and is controlled via a line from a firstworking output of the electronic circuit, and a shut-off valve iscontrolled via a line from a second working output of the electroniccircuit, wherein the measuring line is connected to a first connectorconnection of a three-way valve, and a second connector is connected tothe vacuum pump via a connector line, and wherein a reversible connectorof the three-way valve is connected to an end of the vacuum sensor. 19.Vacuum-packaging machine according to claim 18, wherein an indicatordevice is connected to a third working output of the electronic circuit,whereby the indicator device visually shows the process result.